1. Field of the Invention
The invention relates to the collection of blood samples for testing. More particularly, the invention relates to an apparatus and method for collecting small volume blood samples while minimizing exposure of the blood samples to ambient air.
2. Description of the Related Art
It is well known to utilize syringes having a movable plunger for collecting blood samples. Syringes have proven to be effective, reliable and safe for collecting blood samples of relatively large volumes. Once a blood sample is collected, it can be introduced into various testing apparatus commonly referred to as "analyzers" for blood gas, co-oximetry, electrolyte, and metabolite analysis, for example. Recently, analyzers have been developed that are capable of accurately analyzing blood samples ranging in volume from 90-250 microliters. Syringes cannot effectively collect samples of such a small volume and thus the use of syringes for collecting blood often results in the collection of excess blood.
In many procedures, such as performing blood gas analyses in neonates, it is desirable to minimize the volume of collected blood samples. Of course, neonates have a very small blood volume. Also, blood gas analysis requires that blood be drawn at frequent intervals. Therefore, it is important to draw samples that are as small as possible to reduce or eliminate blood waste and the potential need for blood transfusions.
U.S. Pat. No. 4,263, 922 is exemplary of patents disclosing instruments and methods capable of drawing small volume blood samples. The instrument disclosed in U.S. Pat. No. 4,263,922 includes a capillary tube, a handle, and a needle assembly. The handle serves as a needle assembly adaptor for coupling the needle assembly to the tube. Blood is drawn through the needle assembly and handle into the tube via capillary action. Subsequently, the needle assembly and the handle are removed from an end of the tube and a separate cap is fitted over each end of the tube to retain the sample in the tube. Since the needle assembly and the handle must both be removed before a cap can be placed over an end of the tube, the collected blood sample is exposed to ambient air for a relatively long period of time while the end of the tube is completely open prior to fitting a cap thereto. Such exposure can negatively affect the accuracy of blood analysis on the sample because of gas exchange due to diffusion. A similar exposure to ambient air occurs when removing the caps and interfacing the tube to a blood analyzer. Also, blood may drip out of the tube in the long period of time that the tube end is open. This can reduce the accuracy of blood analysis and can present issues of disease transmission to medical personnel collecting and otherwise handling the blood sample.